! 54 



HARDWICKE'S SCIENCE-GOSSIP. 



interesting features in the structure of the eyes, and 

 particularly of their lenses, which appear to have 

 hitherto escaped the notice of anatomists, and to 

 which no reference is made in the latest considerable 

 contribution to our knowledge of this interesting order 

 of Crustacea. 



The eye of Squilla raphidca, the largest species of 

 its genus, is composed of two huge cylindrical lobes 

 of nearly equal size. The inner and shorter of these is 

 directed inwards, upwards, and forwards, while the 

 outer and longer takes an exactly opposite direction, 

 and looks outwards, downwards, and backwards. 

 When the eye is viewed as a whole in profile, its two 

 lobes are seen to be separated from one another by a 

 wide and shallow obtuse-angled groove, which if 

 continued backwards on to the upper surface of the 

 peduncle would bisect the obtuse-angled distal 

 extremity of the peduncle, which is shaped like the 

 two-way piece from which the bronchi fork in a 

 windpipe. As in most arthropods in which the lens 

 is divided into facets, the lens-facets of the stomato- 

 pod eye are hexagonal. When a strip of the lens of 

 Squilla raphidca including portions of each lobe and 

 of the dividing groove is viewed under the micro- 

 scope, two rows of lens-facets in the bottom of the 

 groove are seen to be elongated in a direction at right 

 angles to the groove, or to the plane dividing the two 

 eye-lobes from one another. The lens-facets are, in 

 fact, modified at the junction of the two eye-lobes. 



The genus Lysiosquilla has eyes much like those of 

 the above-named member of the genus Squilla, with 

 the eye-lobes produced on each side of the interlobar 

 plane and divided from one another by a shallow 

 groove. In L. maculata, giant of its genus, the 

 ordinary hexagonal lens-facets of the two eye-lobes 

 are divided from one another by a band of six 

 longitudinal rows of smaller and differently-shaped 

 facets arranged in oblique series of six. Some of 

 these facets are hexagonal, others are rhomboidal, and 

 a few are irregular in shape ; they are all, however, 

 obvious modifications of the hexagon. 



In the genus Pseudosquilla, the lobes of the eyes 

 are scarcely at all produced, and the lens is not 

 perceptibly divided into lobes. A band of different 

 coloration from that of the surface on each side of it 

 can, however, be made out by the unaided eye 

 crossing the lens from the distal edge of the non- 

 faceted peduncle above to the corresponding point 

 below. Under the microscope, this band is resolved 

 into six longitudinal rows of square and transversely 

 oblong lens hexagons arranged in almost perfect 

 cross series of six. 



The eye of Gonodactylus chiragra is sub-cylindrical ; 

 the lens occupies, roughly speaking, the outer apex 

 of the peduncle, as in many Decapod Crustacea, and, 

 there is no appearance of division into lobes. Never- 

 theless, a band similar to that met with in Pseudo- 

 squilla, which all zoologists admit to be closely allied 

 to Gonodactylus, is present, and is similarly resolvable 



under the microscope into six longitudinal ridges each 

 formed of lens-facets which are elongated in a 

 direction at right angles to the band, and have almost 

 entirely lost all traces of their former hexagonal shape. 

 This band traverses the longer surface of the oval eye, 

 dividing it into two equal parts, which correspond 

 without doubt to the eye-lobes of Squilla raphidca. 

 In this species of Gonodactylus, the two lobes of the 

 lens participate equally in the formation of the one 

 apex of the eye, the two lobes being extended equally 

 in the one forward direction instead of in two opposite 

 lateral directions. But in Gonodactylus gracilis and 

 its allies, the two lobes are so swollen laterally 

 inwards and outwards, that the whole eye has come 

 to resemble a fat pea. This lateral extension of the 

 eye-lobes, carried a few degrees further, would pro- 

 duce an eye of the form and proportions of that of 

 Squilla raphidca. 



In Protosquilla, which has recently been founded by 

 Brooks for the reception of some species that had pre- 

 viously been associated with Gonodactylus, the eyes, 

 as might be expected, differ in matters of the minutest 

 detail only from those of Gonodactylus chiragra. 



Of the remaining genera of Stomatopoda, Lepto- 

 squilla, Chloridella, and Coronida, the first is still very 

 rare, and, being only represented in the collection 

 under my charge by one very young specimen of its 

 single species, has not been examined, but from its 

 general structure, it may, with tolerable confidence, 

 be inferred that in the adult condition it resembles 

 Squilla in the form and arrangement of its lens-facets ; 

 the second, which has such small and degenerate, 

 though, strange to say, strongly bilobed, eyes that 

 nothing can be made out about its lens-facets, is such 

 a very slight modification of the Squilla type that it 

 may be safely set down as having once had eyes like 

 those of Squilla ; and of the last, which has de- 

 generating, but nevertheless also strongly bilobed, 

 eyes, I only possess badly preserved specimens, in 

 which, however, I feel fairly sure that I can detect, 

 between the lens-lobes, traces of a narrow granulated 

 band which may represent an arrangement similar to 

 that seen in Lysiosquilla maculata. 



Both in longitudinal section at right angles to the 

 lens-band and in transverse section, the soft structures 

 of the eyes present no less distinct signs of duplicity 

 than do their lenses, and, in Gonodactylus chiragra 

 and some species of Squilla, exhibit a nearly perfect 

 bilateral symmetry ; the retinuku and vitrella;, es- 

 pecially the former, being disposed plainly in three 

 groups, two lateral corresponding to the two lobes of 

 the lens, and one medium corresponding to the 

 dividing band of modified lens-facets, in size as in 

 number ; and each lateral group of retinulce being 

 separated from the median by an interval which is 

 wider than the large median retinulre are broad. Each 

 of these intervals is in Gonodactylus chiragra occupied 

 by the branches of one of two large blood-vessels 

 | which enter the eye, one on each side of the middle 



